The invention relates to a rheometer or rheometer attachment which is used to measure the viscosity and stress relaxation of polymers, elastomers, and rubber compounds in simple extension. More specifically, the present invention relates to the utilization of a dual windup drum method to characterize the extensional flow behavior of one or more material samples simultaneously.
Joachim Meissner, in the review article xe2x80x9cPolymer Melt Elongation-Methods, Results, and Recent Developmentsxe2x80x9d in Polymer Engineering and Science, April 1987, Vol. 27, No. 8, pp. 537-546 describes different extensional rheometers that have been developed in the prior art. Meissner is also the author of several patents on the subject including U.S. Pat. No. 3,640,127, dated Feb. 8, 1972, German 2,138,504, dated Aug. 2. 1971, German 2,243,816, dated Sep. 7, 1972 and U.K. 1,287,367.
Extensional rheometer designs by Cogswell, Vinogradov, and later Muinstedt had in common that one end of the polymer fiber or filament that was used for testing was fixed to a load cell/indicator, while the other end was stretched by mechanical means to a finite maximum elongation. Accordingly, these rheometers operated with a non-uniform extensional rate throughout the sample particularly near the clamped ends of the fiber. Meissner overcame these difficulties with his dual rotary clamp design in which rotary clamps stretched the fiber at either end over a fixed gauged length. See, for example, xe2x80x9cRotary Clamp in Uniaxial and Biaxial Extensional Rheometry of Polymer Meltsxe2x80x9d by J Meissner, et al., Journal of Rheology, Vol. 25, pp. 1-28 (1981) and xe2x80x9cDevelopment of a Universal Extensional Rheometer for the Uniaxial Extension of Polymer Meltsxe2x80x9d, by J Meissner, Transactions of the Society of Rheology, Vol. 16, No. 3, pp. 405-420 (1972). In a further development of this type of rheometer, in order to improve the transfer of the circumferential speed of the clamps to the local speed of the sample at the location of clamping (strain rate lag), two rotary clamps in the prior art devices were replaced by Meissner and Hostettler as illustrated in xe2x80x9cA New Elongational Rheometer for Polymer Melts and other Highly Viscoelastic Liquidsxe2x80x9d, Rheological Acta, Vol. 33, pp. 1-21 (1994) with matched/grooved, metal conveyor belts. With this design, however, a measurement was limited to a single rotation of the clamps corresponding to a Hencky strain of seven, and the maximum extensional rate was limited to 1/s (a reciprocal second). The extensional viscosity was determined from the force required to deform the fiber, which was measured by the deflection of leaf springs supporting one set of rotating clamps. However, as has been reported in the literature by Erik Wassler in xe2x80x9cDetermination of true extensional viscosities with a Meissner-type rheometer (RME)xe2x80x9d, Proceedings of the 15th Annual Meeting of the Polymer Processing Society, Paper 200 (1999), there can be large deviations between the nominal and the true extensional strain with this type of extensional rheometer due to sample slippage between the rotating clamps.
Other techniques used to measure extensional viscosity involved winding one end of a fiber around a drum and measuring the resultant stretching force at the other fixed end of the fiber, as described in an article by R. W. Connelly, et al., xe2x80x9cLocal Stretch History of a Fixed-End-Constant-Length-Polymer-Melt Stretching Experiment,xe2x80x9d J. Rheol., Vol. 23, pp. 651-662 (1979). Like the earlier designs, this method imparts a non-uniform extensional deformation to the free gauge length of the stretched fiber, particularly at the fixed end of the fiber that can lead to a false material rupture condition during extension.
There remains a need to measure extensional viscosity and stress relaxation of one or multiple polymers, elastomers, and rubber compounds in uniaxial extension simultaneously. Steps to overcome the latter limitations were disclosed in PCT Publication No. WO00/28321 entitled Dual Windup Extensional Rheometer by Martin Sentmanat and having a common assignee with the present invention. Setting out to improve upon the shortcomings of sample slippage and the non-uniform deformations encountered with other extensional rheometer designs, Sentmanat in PCT Publication No. WO00/28321 described an apparatus in which both ends of a material sample are wound around a set of mechanically coupled counter-rotating drums housed in a torque armature. Upon stretching the sample, the extensional resistance of the material sample hinders drum rotation, and the extensional flow behavior of the sample material can be characterized by monitoring the torque on the torque armature required to rotate the windup drums at a fixed rate of rotation. Like the earlier designs, the rheometer described in WO00/28321 is only capable of assessing a single sample material at a time. In addition, because the master and slave drums of the device described in WO00/28321 are both mounted on bearings within the torque armature, friction from the bearings due to the rotation of the master and slave drums contribute to the measured signal during an experiment.
There remains a need to provide a rheometer that can measure a plurality of samples at one time and measures the samples with torque signals that do not include friction from bearings supporting the drums.
According to an embodiment of the present invention, there is disclosed an extensional rheometer apparatus for measuring the extensional flow response of samples of material, such as a low modulus solid sample. The rheometer comprises a primary windup drum mounted to a power drive device for rotating the primary windup drum; a secondary windup drum rotatably mounted in proximity to the primary windup drum; means interconnecting the primary windup drum to the secondary windup drum whereby rotation of the primary windup drum by the power drive device causes the rotation of the secondary windup drum; and a load sensing device for measuring the response of the extensional flow of a low modulus solid sample secured to the primary windup drum and the secondary windup drum.
Further, according to the present invention, the primary and secondary windup drums are preferably in substantially parallel alignment. Further, the means for interconnecting the primary and secondary windup drums are first and second gears individually attached to the primary and secondary windup drums and intermeshed such that the primary and secondary windup drums are counter rotating and cause the primary and secondary windup drums to rotate at the same speed.
Also, according to the present invention, the load sensing device is attached to the secondary windup drum for supporting the secondary windup drum. In an alternative embodiment, the load sensing means is attached to the primary windup drum driving means.
According to another embodiment of the present invention, an extensional rheometer apparatus for measuring the extensional flow response of samples of material, such as a plurality of low modulus solid samples, comprises a primary windup drum mounted to a power drive device for rotating the primary windup drum; a plurality of secondary windup drums rotatably mounted in proximity to the primary windup drum; means interconnecting the primary windup drum to the plurality of secondary windup drums whereby rotation of the primary windup drum by the power drive device causes the rotation of the secondary windup drums; and a load sensing device attached to each of the secondary windup drums for supporting each of the secondary windup drums and measuring the response to the extensional flow of low modulus solid samples secured to the primary windup drum and each of the plurality of secondary windup drums.
Further, according to the latter embodiment of the present invention, the primary and plurality of secondary windup drums are in substantially parallel alignment. Also, the means for interconnecting the primary and plurality of secondary windup drums are first and second gears individually attached to the primary and plurality of secondary windup drums and intermeshed such that the primary and plurality of secondary windup drums are counter rotating and rotate at the same speed.
According to another embodiment of the present invention, an extensional rheometer apparatus for measuring the extensional flow response of samples of material, such as a low modulus solid sample, comprises a primary windup drum mounted to a primary power drive device for rotating the primary windup drum; a secondary windup drum rotatably mounted to a secondary power drive device for rotating the secondary windup drum in proximity to the primary windup drum; and a load sensing device attached to the secondary power drive device for supporting the secondary windup drum and measuring the extensional flow response of a low modulus solid sample secured to the primary windup drum and the secondary windup drum. The load sensing device is secured at one end to a support member and at the other end to the secondary power drive device.
According to yet another embodiment of the present invention, an extensional rheometer apparatus for measuring the extensional flow response of samples of material, such as a of low modulus solid samples comprises a primary windup drum mounted to a primary power drive device for rotating the primary windup drum; a plurality of secondary windup drums rotatably mounted to a plurality of secondary power drive devices for individually rotating the secondary windup drums in proximity to the primary windup drum; and a plurality of load sensing devices, each attached to one of the plurality of secondary power drive devices for supporting the plurality of secondary windup drums and measuring the extensional flow response of low modulus solid samples secured to the primary windup drum and each of the secondary windup drums. Each of the plurality of load sensing devices are secured at one end to a support member and at the other end to one of the plurality of secondary power drive devices.
According to yet another embodiment of the present invention, a method for measuring the extensional flow response of a material, such as a low modulus solid sample comprising the steps of: rotating a primary windup drum with a power drive device; rotating a secondary windup drum in proximity to the primary windup drum; and supporting the secondary windup drum and measuring the extensional flow response of a low modulus solid sample secured to the primary windup drum and the secondary windup drum with a load sensing device. The method includes the steps of rotating a plurality of secondary windup drums in proximity to the primary windup drum; and supporting the plurality of secondary windup drums and measuring the extensional flow response of a plurality of low modulus solid samples secured to the primary windup drum and the plurality of secondary windup drums with a plurality of load sensing devices each attached to the plurality of secondary windup drums.